Signaling system



March 28, 1944.

C. E. LOMAX P. B. x. lswn'm-NaoARD |s SIGNALING SYSTEM Filed April 26, 1941 2 Sheets-Sheet 1 v GROUP SELECT KEYS INV ENT OR.

CLARENCE E. LOMAX ATTO R NEYS March 28, 1944. C. E LOMAX 2,345,136

SIGNALING SYSTEM Filed April 26, 1941 2 Sheets-sheet 2 269 267 266 l l VERT l ROT 2|| l l, 27o l CONNECTOR 2| .l 24| 20| 4mm R240 .PULSE clRculT l5 202 R220 TRANSFER CUT-OFF f SIGNAL R200 R210 L 9 CONNECTOR T OTHER O b slGNALs INVENTOR. CLARENCE E. LOMAX BYMMA/,M #MZL ATTORNEYS Patented Mar. 28,1944

UNITED .sTArs .PATENT OFFICE SIGNALING SYSTEM cin-ense amm Lomax. ou Park, n1., assignmto Automatic Electric Laboratories, Inc., a corporation o! Delaware Application April ze, 194i, serial No. 390,596

4 clnmsl 'I'he present invention relates to signaling systems and, more particularly, to improvements in annunciator systems of the character used in hospitals, nurses homes and the like for selectively calling the employes and other members of the hospital stall.

It is an object of the present invention to provide an improvedsystem of the character described, which is simple in arrangement, is economical to install, and requires only a small amount of equipment in order to provide for the selective control of a large number of signals.

It is a further object of the invention to provide an improved system of the character described, in which each signal device may be selectively controlled -by differently coded signals to produce any one of a plurality of different indications.

It is another object of the invention to provide an improved system of the character described. wherein the selection of the general location of a desired signal device, as well as the selection of the coded signals to be utilized in controlling the device, are prerequisites to the final selection of the device.

According to another object of the invention. the transmission of a selceted coded signal to a desired signal device is eilected automatically incident to the nal selection of the device.

In the illustrated embodiment oi the invention change switchboard, which keys individually correspond to the signal codes that are utilized in energizing the signal devices which may be selected through the automatic switch. The arrangement is such that the group select and code select keys jointly controla pulsing circuit which may be set up between the calling device and the automatic switch for the purpose of directively controlling this switch. 'More specifically, the actuation of a selected code select key and a selected group'select key is a prerequisite to the operation ofthe calling device to control the automatic switch.

`The novel features believed to be characteristic of the invention are set forth with particularity in the appended claims. The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the specification taken in connection with the accompanying drawings in which Figs. 1 and 2, when laid side by side in the order named, illustrate a portion of the equipment provided in a system having embodied therein the features of the signal devices. which may be located in the diierent rooms of a nurses home, for example, are arranged in groups and are accessible to an automatic switch for control purposes. This automatic switch is provided with a plurality of settings which individually correspond to difierent signals in each of the several groups and is connected over a plurality of control paths, also individually corresponding to the signal groups, with a control panel located at the branch telephone exchange switchboard which serves the nurses home and possibly adjacent, hospital buildings. A plurality of group select keys are provided at thebranch exchange switchboard which individually correspond to the different groups of signals and are each operative to select the control path of the switch which corresponds to the associated signal group. The branch exchange switchboard is also equipped with a calling device which is operative to direct the automatic switch to a setting wherein a. desired signal in one group, as well as a corresponding signal in each of the other groups, is selected. Code select keys are also provided at the branch exthe invention as briefly outlined above.

Referring now more particularly to the drawings, the system there illustrated comprises a plurality of audible signals I3, 6| I, etc., which may be in the form of buzzers or the like and are individually provided in the diierent rooms of a large nurses home or hospital. For control purposes, these signals are arranged in groups of one hundred each, and when the illustrated system arrangement is utilized a maximum of twelve hundred signals may be controlled. These signals are controlled through a pair ofl connectors 2| i and 2 2 by switching equipment provided at the.

private branch exchange switchboard I5 of the telephone system which serves the nurses home and any other buildings of the same organization.

' Briefly described, this equipment includes a strip of twelve group select keys i6 which are individual to the twelve diierent groups of signals, three code select keys |4I, |42 and |43, a ringing key |44, a release key |45, a code transmission key |46 and a calling device l1 of the well-known dialoperated type. This calling device conventionally includes a pair of shunt springs Ila, which are moved into engagement when the dial of the device occupies an oil-normal position, and a pair of pulsing springs Hb. The keys |4| to |45, inclusive, constitute a single strip and are mechanically interlocked in a well-known manner, so that when any one of the first four thereof is operated to until the release key I 46 is momentarily operated toits release position. The mechanical arrangement of such interlocking mechanisms is well known in the art, The keys forming the group select strip I6 are also mechanically interlocked to prevent the operation of more than one key at a time. More specifically, the arrangement of the mechanical interlock mechanism incorporated in this strip is such that when one of the twelve keys is depressed it remains in this depressed position until another key is depressed, at which time the first actuated key is automatically released. The branch exchange switchboard is also equipped with a pair or pilot lamps |41 and |40 which are indiviidual to the two connectors 2| and 22 and serve to indicate the busy condition thereof.

For the purpose of providing differently coded signal currents, which may `selectively be used to energize a selected one of the signals, a cyclically ,operative code interrupter I of conventional arrangement is provided. This inter-v rupter may be of the well-known all-relay typeor of the rotary type, as desired. Briefly described, this interrupter is provided with circuit control contacts which function to connect the three code leads |35. '|00 and |31 to the undergrounded terminal of the ringing current generator l0 for differently coded intervals of each code cycle. Successive code cycles are separated by spacing intervals, and during each oi' these intervals a ground pulse is transmitted over the pickup lead |34. The control apparatus provided in association with the above-described switching equipment located at the branch exchange switchboard includes a slow-to-release start relay RI I0, a ring start relay RI00, and a pair of digit counting relays R|20 and R|20. The three lastmentioned relays are of the well-known doublewound, two-step type.

As indicated above, the selection and selective control of the various signals is effected through the provision of the connectors 2| and 22 which are of identicalarrangement, but have access to different groups of the signals. Briefly described,

the connector 2| comprises a two-motion switching mechanism of the well-known Strowger This mechanism is equipped with six banks of contacts each of which includes one hundred contact points which are individually connected to different signals. The contacts making up this contact ileld are divided into ten levels of ten each, and each of the six banks has A therewith one of the six wipers 20| to 260, inclusive. For the purpose of elevating these wipers to a position opposite a desired contact level, and then rotating the same into engagement with a selected contact set of the selected level, vertical and rotary magnets 261 and 264 are included in the switching mechanism. The

ted

mechanism further comprises a release vmagnet v slow-to-release digit relays R200 and R240, and' its o-normal position it remains in this position a pulse circuit cut-oil relay R260. These relays are connected and arranged to operate in the manner described immediately below.

Current for energizing the two* pilot lamps |41 and |44, the various control relays and the operating magnets of the two Strowger switching mechanisms, is supplied from a common direct current source, the positive terminal of which is connected to a common bus conductor and to ground.y The opposite terminal of this source is connected to a common negative bus conductor which terminates the connections from the various relay, magnet and lamp terminals identified in the drawings by the negative polarity sign. For convenience in describing the circuits involved, the source of current, which may conventionally comprise the exchange battery serving the branch exchange, has not been shown.

In considering the operation of .the system, it

.may be assumed that the operator attending the branch exchange switchboard I5 receives a call for one of three nurses occupying the room in which the signal I3 is located, and that the desired nurse is assigned the rst code as a call signal. In order to call this nurse the operator at the switchboard I5 first actuates the key I4I ,to select the iirst code, and actuates the group select key I to select the iirst group of signals in which the desired signal I3 is included. After these operations are performed, the operator may actuate the calling device I1 to direct the wiper 26| into engagement with the contact terminating the lead |3a extending to the signal I2. When the No. I code key |4| is operated to its oH-normal position, the contacts |4Ib thereof are closed to complete an obvious circuit for energizing the start relay RIIO. At the contacts |4|a a circuit is prepared for transmitting ringing current of the nrst code over the ringing lead |54 and the control path IGI. Thelatter circuit is further prepared at the contacts Ib when the group select key I is operated to its olf-normal position. At the contacts Ia of this key a circuit is prepared for transmitting impulses to the connector 2| from the calling device I1.

The start relay RI I0, upon operating, closes its contacts 2 to connect the interrupter start lead |30 to ground, whereby operation of the code interrupter I8 is initiated. At its contacts the relay RI I0 prepares a locking circuit for each of the three relays RI00, R|20 and RI30. At its contacts I I3, the relay Rl I0 completes the abovementioned pulsing circuit over winch the line relay R200 is energized. This circuit extends from ground by way of the pulsing springs I'Ib, the contacts H3, the common pulsing lead I5I, the contacts Ia. of the key I, the conductor |52 and the winding of R200 to battery. When this circuit is completed the relay R200 closes its contacts 202 to complete an obvious circuit for energizing the hold relay R2I0. At its contacts 20|, the relay R200 opens a point in the common portion of the operating circuits for the Vertical magnet 261, the' rotary magnet 268 and the two relays R220 and R230. The relay R2|0, in operating, closes its contacts 2|2 to prepare a locking circuit for the cut-off relay R250. At its contacts 2| I, the relay R2I0 opens a point in the incomplete operating circuit for the release magnet 269. At its contacts 2|3, the relay R2|0 further prepares the common portion of the operating circuits for the vertical magnet 261, the rotary magnet 268 and the two relays R220 and R220. Following the operation of the hold relay R2|0.

to 266, inclusive.

the connector 2| is conditioned to respond to impulses transmittedthereto through operation ci' the calling device '|1. pointed out that the lead |3a extending to the signal device |3 is connected to the third contact of the top bank in the i'lrst level of contacts of the contact eld associated with the wipers 26| Accordingly, the directory number assigned to this signal is 13.

When the first digit .1 is dialed at the switchboard f the pulsing springs |1b are opened and closed to transmit a single impulse over the above-traced pulsing circuit to the line relay R200. Incident to the off-normal movement of the dial of the calling device |1, the shunt springs |1a are also closed to complete a circuit including the contacts |3| for energizing the upper winding of the digit counting. relay Rl30. When this circuit is completed, the relay R|30 partially operates to close only its preliminary make contacts |33, whereby a path including the shunt springs |1a and the contacts |3|, |33 and lll, is completed for short-circuiting the lower.

winding of this relay. The relay R200, upon restoring at the beginning of the open-circuit period of the impulse, closes its contacts 20| to complete the prepared circuit for energizing the transfer relay R220 and 'the vvertical magnet 261 in series. This circuit extends from ground by way of the contacts 20| and 2|3, the off-normal contacts 212, the winding of R220 and the winding of the vertical magnet 261 to lbattery. When energized in this circuit the relay R220 opens its contacts 222 to prevent the impulse or impulses of the first digit from being transmitted to the rotary magnet 268. At its contacts 22|, the relay R220 prepares a pulse circuit by-pass for maintaining the pulsing circuit through the vertical magnet 261 in case the rst digit transmitted to the connector 2| comprises more than one impulse. rIhe vertical magnet 261, upon operating, elevates the wiper carriage structure of the Strowger switching mechanism one step so that the wipers 26| to 266, inclusive, are positioned opposite the rst level of bank contacts in the associated contact field. Incident to this vertical movement of the wiper carriage structure the off-normal springs 210 are moved into engagement to complete an obvious circuit for energizing the pilot lamp |41; the off-normal springs 214 are closed to prepare the operating circuit for the release magnet 269; the ofi-normal contacts 212 are moved out of engagement to interrupt the initially completed circuit for energizing the series-connected windings of the vertical magnet 261 and the transfer relay R220; and the off-normal contacts 213 are moved into engagement to complete the above-mentioned by-pass pulsing circuit through these series-connected windings. In this regard, it will be noted that if the rst digit dialed through operation of the calling device |1 comprises more than one impulse, all impulses which follow the ilrst impulse are repeated by the line relay R200 to the transier relay R220 andthe vertical magnet 261 over a circuit which includes the contacts 20|, 2|3, 213 and 22 I.

During the inter-digit pause between the rst and second digits, `the line relay R200 retains its operated position to cause the deenergization and release of the transfer relay R220. In this regard, it is pointed out that, due to the slow-torelease of the transfer relay R220. In this re- R2|0 and the transfer relay R220 do not follow currentv pulses transmitted thereto through op- In this regard, it iseration of the line relay R200. Accordingly. the hold relay R2|0 retains its operated ,position Athroughout the dialing ofthe two digits, and the transfer relay R220 remains operated whenim- 5 pulses are being transmitted therethrough to the vertical magnet 261. Upon restoring at the end of the first digit under consideration, the transfer relay R220 opens its contacts 22| to prevent the impulses of the second digit from being transmitted to the vertical magnet 261, and closes its contacts 222 to prepare the previously mentioned circuit for transmitting current pulses through the winding of the digit relay R230-to the rotary magnet 268.

As indicatedabove, when the dial of the calling device |1 is returned to its normal position at the end of the rst digit, the shunt springs |1a are disengaged. Incident to the separation of these springs the path short-circuiting the lower winding of the digit counting relay R|30 is interrupted, permitting the two windings of this relay to be energized in series over a circuit which includes the contacts and 33. When this series circuit is completed the relay R|30 completes its operation, andvin so doing opens its contacts |3| further to interrupt its operating circnt as traced above. At its`contacts |32, the relay R|30 prepares the operating circuit for the second digit counting relay R| 20. When the second digit 3 is dialed at the switchboard |5 through operation of the calling device |1, the shunt springs |1a are again moved into engagement and the pulsing springs |1b are opened Iand closed three times to transmit three impulses to the line relay R200. Incident to the engagement of the shunt springs lla, the prepared operating circuit for the digit counting relay R|20 is completed, this circuit including the contacts |32 and |22. The relay R|20 now partially operates to close only its preliminary *make contacts |23, whereby a path including these contacts and the additional contacts. |22 and |32 is completed for short-circuiting the lower winding of the relay. l

The line R200 follows the three impulses of the Asecond digit. and functions to repeat the same over the above-mentioned pulsing circuit to the rotary magnet 268. This circuit may now be traced as extending from ground by way of the contacts 20|, 2|3, 213 and 222, the winding of R230, the contacts 252, and the winding of the magnet 268 to battery. When initially energized in this circuit, the relay R230 closes its contacts 232 to complete an obvious circuit for energizing the digit relay R240. At its contacts 23|, the relay R230 opens the incomplete operating circuit for the pulse circuit cut-oil relay R250. The last-mentioned circuit is prepared at the contacts 24| incident to the'operation of the relay R240. Due to the slow-to-release characteristics thereof, the two digit relays R230 and R240 retain their operated positions until shortly after the end of the second digit. Each time a current pulse is transmitted to the rotary magnet 268 over the above-traced pulsing circuit, this magnet operates to rotate the wiper carriage` structure one step. Accordingly, the six wipers 26| to 266, inclusive, are positioned to engage the third contacts of the iirst contact level in the associated contact field, at the end of the second digit. With theconnector switch wipers in this-position, the wiper 26| engages the contact which terminates the lead |3a extending to the desired signal |3. At the end of the second digit, the line relay R200 retains its operated position to cause the deenergization and release oi the digit relay R230. In releasing, the relay R230 opens its contacts 232 to deenergize the digit relay R240. and closes its contacts 23| to complete the prepared operating circuit for the pulse circuit cut-oi! relay R250. The relay R250 now operates and locks to ground over a path. including the contacts 25| and 2| 2. At its contacts 252, the relay R250 opens the pulsing circuit tothe rotary magnet 283, whereby furthr operation of the line relay R200 is rendered ineffective to produce further movement of the wiper carriage structure. `Shortly following the operation 'of the pulse circuit cut-oi! relay, the digit relay R240 restores and opens its contacts 24|". Thus the release of the pulse circuit cut-oil relay R250 is transferred to the control of the hold relay R2 0.

As the dial of the calling device I1 returns to its normal position to conclude the second digit, the shunt springs I'la are opened to interrupt the path short-circuiting the lower winding of thedigit counting relay R|'20,permitting the two windings of this relay to be energized in series over a circuit which includes the contacts III .and |23. When its two windings are thus energized, the relay R|20 completes its operation and closes its contacts |2| to prepare the operating circuit for the ring start relay RIUII.r At its contacts |22, the relay R|20 opens its operating circuit as traced above. When the code interrupter I3 next operates to transmit a ground pulse over the pickup lead |34, the upper winding of the ring start relay R| is energized in a circuit which includes this lead and the contacts |2| and |04. When thus energized the relay R|00 partially operates Ato close only its preliminary make contacts |05, thereby to complete a path through the contacts I I for short-circuiting its lower winding. At the end of the pickup pulse the lead |34 is disconnected from ground, permitting the two windings of the ring start relay R|00 to be energized in series over a circuit including the contacts and |05. When thus fully energized' the relay RI00. completes its operation. At its contacts |04, the relay R|00 opens the pickup pulse circuit over which its upper winding was linitially energized. At its contacts |0I, |02 and |03, the relay R|00 extends the three code leads |35, |36 and |31 to the contacts of the code select keys I4I, |42 and |43, respectively. Incident to the last-mentioned operation, a circuit is completed for energizing the selected signal I3 each time the code interrupter I8 functions to connect the selected code lead |35 to the ungrounded terminal of the ringing current generator I9. This circuit may be traced as extending from the grounded terminal of the generator I9 through the windings of the signal I3 and by way of thev conductor |3a, the wiper 26|, the control path I6 I the contacts Ib, the common ringing lead |54, the contacts |4|a and |03, the code lead |35, and the contacts of the code interrupter I8 to the ungrounded terminal of the generator I9. 'I'he signal I3 responds to the current traversing this circuit by producing an audible coded signal which indicates to one of the three occupants of the room in which this signal is located that she is being called from the branch exchange switchboard .|5. The called nurse may proceed to the nearest telephone substation and call the operator attending the'switchboard I5 for the purpose of acknowledging the coded call.

When the transmitted signal is thus acknowledged over the telephone communication facilities, the operator attending the switchboard I VIIS may release the operated switching equipment by momentarily actuating the, release key |45 to its otr-normal position. .(s explained above, when this key isoperated, the code select key |4| is automatically released and assumes its normal position wherein the contacts I4|a and |4Ib are respectively disengaged.. At the contacts I4Ia, the above-traced circuit over which ringing current is transmitted to the signal I3 is interrupted to terminate the signaling operation in progress. At the contacts |4 Ib, the operating circuit for the start relay RI |0 is opened. The relay RI I0 now restores and opens its contacts to cause the deenergization and release of the three relays RI00, R|20 and RI30. At its contacts II2, the relay RI I0 disconnects the interrupter start lead |33 from ground, whereby operation of the code interrupter I3 is arrested.' At its contacts I|3, the relay RI I0 opens the previously traced operating circuit for the line relay R200.

When the relay R200 restores it opens its contacts 202 to cause the deenergization and release of the hold relay R2I0. 'I'he latter relay, upon restoring, opens its contacts 2 I 2 to cause thedeenergization and release of the pulse circuit cut-oi! relay R250, and closes its contacts 2| I to complete the prepared operating circuit for the release magnet 269. This magnet, in operating, attracts its associated holding pawl, whereby the Wiper carriage structure of the Strowger switching mechanism is returned to rotary and vertical normal, in the usual manner. Incident to the iinal movement of the wiper carriage structure towards its normal position, the off-normal springs 210 are disengaged to deenergize the pilot lamp |41; the oiI-normal springs 214 are disengaged to deenergize the release magnet'269; the

'oiI-normal contacts 212 are moved into engagement to reprepare the operating circuit for the vertical magnet 261; and the off-normal contacts 213 are disengaged. Following the release of the connector 2|, in the-manner just explained, all of the equipment utilized 1n selecting and controlling the signal I3 is restored to normal, with the exception of the group select key I. In this regard, it will be understood that there is no necessity for releasing this key until another group select operation on the part of the operator attending the switchboard I5 is required. Thus the majority of the calls may be intended for the signals forming the first group accessible to the connector 2|, in which case the key may be retained in its operated position more or less indefinitely.

From the foregoing explanation it will be understood Vthat through selective operation of the group select keys I6 and the three code select keys |4I, |42. and |43, accompanied by selective operation of the calling device |1, any one of the twelve hundred signals may be controlled to produce three diierent signal indications. In order to amplify this statement it'may be pointed out that if the signal assigned the directory number 345, for example, is to be used in calling a nurse having the third code assignment, the group select key 3 and the code select key |43 are iirst operated, after which the two digits 4 land "5 are successively dialed through operation of the calling device I1. 'I'he manner in which the desired signal 345 is selected in response to these operations will be clearly apparent from the foregoing explanation. In this case, however, the third control path |63 through the connector 2| is utilized in transmitting signal current to the .selected signal. It will also be apparent from the only utilized in selecting signals in the rst six groups. The connector 22, on the other hand, may be controlled through the group select keys 'I to I2, inclusive, to select any one of the signals in the last six groups, i. e., the signals assigned the directory numbers 60| to |200, inclusive. The manner in which this connector operates, when controlled from the branch exchange switchboard I5, is exactly the same as described above with reference to the connector 2|.

In any case where the operator attending the switchboard I5 desires to transmit a specially, coded set of ringing current pulses to a selected signal, the ring key |44 and the code transmission key |46 are used. In this connection, it will be apparent that the contact springs |44b of the ring key |44 control the start relay RI I0 in the same manner as the corresponding springs of the code key I4I. After a signal, such, for example, as the signal I3, has been selected through operation `of the calling device I'I, in the manner previously explained, the operator may manually actuate the key |46 in accordance with the particular code which designates the desired person. In this case, the circuit traversed by the signaling current extends from the ungrounded ter-V minal of the generator I9 by way of the contacts of the key |46, the contacts |44a, the conductor \|54, the contacts Ib, the control path 6|, the wiper 26|, the conductor |3a, and the windings of the signal I3 to the grounded terminal of the generator I9. The manner in which the operated switching equipment is released, after the manual transmission of a particular code through actuation of the key |46, is exactly the same as described previously with reference to the transmission of signaling current of the rst code to the signal I3.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modiilcations may be made therein, and it is contemplated to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

l. In a signaling system, a control station, a plurality of signals arranged in groups, an automatic switch having a plurality of settings individually corresponding to dierent signals in each of said groups, a plurality of control paths individually corresponding to said groups and each extending from said station to said switch, a calling device at said station operative to direct said switch to a selected setting wherein` said control paths are extended to the signals which correspond to the selected setting, a plurality of group select keys at said stations which individually correspond to said groups, means for producing diierently coded signal currents, code select keys at said station which individually correspond to said codes, a circuit jointly controllable by any one of said group select keys and any one of said code select keys for rendering said switch controllable by said calling device. means responsive to the operation of one of said group select keys for selecting the control path individual to the signal group which corresponds to the operated group select key, and a circuit controlled by'the operated code select key for transmitting signal current of the selected code ma the selected control path to the selected 2. In a signalling system, a control station. a plurality of signals arranged in groups, an automatic switch having a plurality of settings individually corresponding to diierent signals in each of said groups, a plurality of control paths individually corresponding to said groups and each extending from said station to said switch, a calling device at said station operative to direct said switch to a selected setting wherein said control paths are extended to the signals which correspond to the selected setting, a plurality of group select keys at said stations which individually correspond to said groups, means for producing diierently coded signal currents, code select keys at said station which individually correspond to said codes, a circuit jointly controllable by any one of said group select keys and any one of said code select keys for rendering said switch controllable by said calling device, means responsive to the operation of one of said group select keys for selecting the control path individual to the signal group which corresponds to the operated group select key, and means jointly controlled by said calling device and an operated one of said code select keys for transmitting signal current of the code corresponding to the operated code select key over the selected control path to the selected signal incident to the operation of said switch to the setting corresponding to the selected signal.

3. In a signaling system, a control station, a plurality of signals arranged in sets, an automatic switch having diierent settings individually corresponding to said sets of signals, a plurality of signal select keys at said station which are individually operative to select different signals of any set of said signals selected through operation of said switch to any one of its settings, means for producing differently coded signal currents, code select keys individual to the different codes and each operative to select the signal current of 1corresponding codes for transmission to a selected signal, a calling device at said station, and means jointly controllable by any one of said signal select keys and any one of said code select keys for rendering said switch controllable by said calling device.

4. In a signaling system, a control station, a plurality of signals arranged in groups, a pair of automatic switches each having a plurality of settings corresponding to different signals ln each of said groups, two sets of control paths which respectively extend from said station to said switches, said control paths individually corresponding to said groups of signals, a calling device at said station operative to direct either of said switches to a selected setting wherein the associated control paths are extended to the signals which correspond to the selected setting, a plurality of keys at said station which individually correspond to said groups of signals, said keys being interlocked to prevent more than one thereot from being operated at a time, means responsive to the operation of any one of said keys for rendering the associated switch controllable by said calling device, means responsive to the operation oi one of said keys for selecting the control path individual to the group which corresponds to the operated key, and means for controlling the selected signal over the selected control path.

CLARENCE ERNEST LOMAX. 

